aliased generic function reference type breaks JS backend

[gavinking]

I can defeat the fix to #3098 via the following code:

Set<Param> getSet<Param>(Set<Param> params, Param next) 
            given Param satisfies Object
        //=> set{next, *params};
        => set(params.sequence().withTrailing(next));

value ref = getSet;

alias Alias => <Param> given Param satisfies Object => Set<Param>(Set<Param>, Param);

Alias fun() => ref;

value mySet = fun()(set{1,2,3},4);

Note that to fix this I might need to get the typechecker to attach some more information to the tree.